Such means have been described in French Patent 2,529,531. This type of seal can be used on certain containers containing, for example, sterile liquid pharmaceutical products for injection. The plug is a tight stopper made of flexible material forced into the opening in the neck of the container and capable of being traversed by the needle of a syringe to remove the product. The cap locking this plug is provided with a notch fitted elastically beneath a shoulder on the neck of the container and with a central opening permitting passage of the needle, and is sealed before use by a tear-off lid attached to it by bonding, heat sealing, or other means and making it possible completely to isolate the plug from external contaminants and thus guarantee the stability of the product contained in the container. This lid is likewise attached to a rigid gripping ring connected to the cap by strips of material and permitting tearing off of the lid in a reliable, easy, and practical fashion using one hand, in order to provide access to the plug via the central opening.
This design, while it does apply to injectables, is not suitable for other sterile pharmaceutical products, for example, powders, for which it is necessary to remove the locking cap completely in order to be able to remove the plug and gain access to the product inside.